Semiconductor device

ABSTRACT

The element electrodes of a semiconductor element are disposed in a cell region, while an outermost peripheral electrode electrically connected to a semiconductor substrate is disposed in a peripheral region. In the peripheral region, a second-conductivity-type layer is disposed above a super-junction structure. A potential division region is disposed above the second-conductivity-type layer to electrically connect the element electrodes and the outermost peripheral electrode and also divide the voltage between the element electrodes and the outermost peripheral electrode into a plurality of stages. A part of the potential division region overlaps the peripheral region when viewed from the thickness direction of the semiconductor substrate.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a U.S. national stage application ofInternational Patent Application No. PCT/JP2012/005577 filed on Sep. 4,2012, and is based on Japanese Patent Application No. 2011-210690 filedon Sep. 27, 2011, Japanese Patent Application No. 2011-263799 filed onDec. 1, 2011, Japanese Patent Application No. 2012-178676 filed on Aug.10, 2012, and Japanese Patent Application No. 2012-178674 filed on Aug.10, 2012, the contents of which are hereby incorporated by reference.

TECHNICAL FIELD

The present disclosure relates to a semiconductor device including acell region and a peripheral region surrounding the cell region.

BACKGROUND ART

Patent Document 1 discloses a semiconductor device including a verticalsemiconductor element having a super-junction (SJ) structure in whichN-type columns and P-type columns are alternately and repeatedly formedin a striped shape in a drift layer. With the SJ structure, an electriccurrent path in which an electric current easily flows is formed,resulting in a lower ON resistance. Also, with the SJ structure, theconcentration of an electric field is avoided so that a high breakdownvoltage is obtained. In other words, both of the high breakdown voltageand the low ON resistance are achieved.

The semiconductor device is provided with a structure in which, in acell region where the vertical semiconductor element is formed, a chargebalance is maintained such that the P-type columns and the N-typecolumns have equal impurity concentrations while, in a peripheral regionsurrounding the cell region, a difference is provided between therespective impurity concentrations of the P-type columns and the N-typecolumns. Specifically, with regard to the difference between theimpurity amount in each of the P-type columns and the impurity amount ineach of the N-type columns, the difference between the impurity amountsin the combination of the P-type column and the N-type column located onthe outermost periphery of the peripheral region is adjusted to besmaller than the difference between the impurity amounts in anothercombination of the P-type column and the N-type column located in theperipheral region, while the difference between the impurity amounts inthe combination of the P-type column and the N-type column located onthe innermost periphery of the peripheral region is adjusted to belarger than the difference between the impurity amounts in a combinationof the P-type column and the N-type column located in the cell region.

PRIOR ART DOCUMENTS Patent Document

[Patent Document 1] JP-A-2006-73615

SUMMARY OF INVENTION Problem to be Solved by the Invention

However, in the semiconductor device shown in Patent Document 1mentioned above, in a direction from the innermost periphery to theoutermost periphery of the peripheral region, a P-rich state where theimpurity concentration of the P-type column is higher than the impurityconcentration of the N-type column is encountered first and then, at aposition closer to the outer periphery, an N-rich state where theimpurity concentration of the N-type column is higher than the impurityconcentration of the P-type column is encountered. When a P-rich regionis formed and P-charges Qp become larger than N-charges to result in apositive charge imbalance (=P-Charges Qp−N-Charges Qn/N-Charges Qn), adepletion layer expands to a drain side (substrate bottom surface side)so that a breakdown occurs on the outermost periphery side. As a result,as can be seen from the relationship diagram between a charge imbalanceand a breakdown voltage shown in FIG. 28, the breakdown voltage is loweron the outermost periphery side than in the cell region so that theperipheral region narrows a charge balance margin for the cell region.This causes the problem of degrading the breakdown voltage yield of thesemiconductor device.

In addition, equipotential lines in the PN-columns are pulled by theP-rich region toward a rear surface side of the substrate. Conversely,in the N-rich region outside the P-rich region, the equipotential linesare pulled toward a front surface side of the substrate.

In particular, the front edges of the equipotential lines in the N-richregion extend toward the front surface side of the substrate. However,since the positions of the front edges are not fixed, the front edges ofthe individual equipotential lines in the N-rich region may possibly beconcentrated on one location. This causes the possibility that theconcentration of an electric field occurs to consequently reduce thebreakdown voltage.

An object of the present disclosure is to provide a semiconductor devicethat can ensure a breakdown voltage without causing concentration of anelectric field on a peripheral region. Another object of the presentdisclosure is to provide a semiconductor device that can restrict theperipheral region from narrowing a charge balance margin for a cellregion and can improve a breakdown voltage yield.

Means for Solving the Problem

A semiconductor device according to a first aspect of the presentdisclosure includes a cell region and a peripheral region surroundingthe cell region, and includes a semiconductor substrate, a semiconductorelement, an element electrode of the semiconductor element, an outermostperipheral electrode, a second-conductivity-type layer, and a potentialdivision region. The semiconductor substrate includes afirst-conductivity-type layer, and first-conductivity-type columnregions and second-conductivity-type column regions formed above thefirst-conductivity-type layer and serving as a drift region. Thefirst-conductivity-type column regions and the second-conductivity-typecolumn regions form a super-junction structure. A part of thesemiconductor substrate is included in the cell region, while other partof the semiconductor substrate is included in the peripheral region. Thesemiconductor element and the element electrode are disposed in the cellregion. The outermost peripheral electrode is electrically connected tothe semiconductor substrate in the peripheral region. Thesecond-conductivity-type layer is formed above the super-junctionstructure in the peripheral region. The potential division region isformed above the second-conductivity-type layer. The potential divisionregion electrically connects the element electrode to the outermostperipheral electrode and also divides a voltage between the elementelectrode and the outermost peripheral electrode into a plurality ofstages. A part of the potential division region overlaps the peripheralregion when viewed from a thickness direction of the semiconductorsubstrate.

The semiconductor device according to the first aspect can ensure abreakdown voltage without causing concentration of an electric field onthe peripheral region.

A semiconductor device according to a second aspect of the presentdisclosure includes a cell region where a semiconductor element isformed, and a peripheral region surrounding the cell region. Thesemiconductor device includes a semiconductor substrate having afirst-conductivity-type layer, and first-conductivity-type columnregions and second-conductivity-type column regions formed above thefirst-conductivity-type layer and serving as a drift region. Thefirst-conductivity-type column regions and the second-conductivity-typecolumn regions form a super-junction structure. A part of thesemiconductor substrate is included in the cell region, while other partof the semiconductor substrate is included in the peripheral region. Inthe cell region, a first-conductivity-type charge amount and asecond-conductivity-type charge amount are set equal. The semiconductorsubstrate further includes a charge balance change region in theperipheral region. In the charge balance change region, thefirst-conductivity-type charge amount in the super-junction structure isgradually increased to be larger than the second-conductivity-typecharge amount toward an outer peripheral direction of the cell region.

The semiconductor device according to the second aspect can restrict theperipheral region from narrowing a charge balance margin for the cellregion and can improve a breakdown voltage yield.

BRIEF DESCRIPTION OF DRAWINGS

The above and other objects, features and advantages of the presentdisclosure will become more apparent from the following detaileddescription made with reference to the accompanying drawings. In thedrawings:

FIG. 1 is a plan view of a semiconductor device according to a firstembodiment of the present disclosure;

FIG. 2 is a cross-sectional view of the semiconductor device taken alongthe line I-I in FIG. 1;

FIG. 3 is a plan view showing guard rings and zener diodes in aperipheral region;

FIG. 4(a) is a plan view in which the widths of P-type column regions inthe peripheral region are changed at an equal rate, and FIG. 4(b) is aplan view in which the widths of P-type column regions in the peripheralregion are continuously changed;

FIG. 5 is a diagram showing the relationship between the length of apotential division region and a breakdown voltage;

FIG. 6(a) is a diagram showing the result of simulation of a potentialdistribution when, in a structure in which the peripheral region is notprovided with the potential division region, the concentration of anN-type impurity in the peripheral region is held constant, and FIG. 6(b)is a diagram showing the result of simulation of a potentialdistribution in a structure in which, in the structure in which theperipheral region is not provided with the potential division region,the concentration of the N-type impurity in the peripheral region iscontinuously changed;

FIG. 7(a) is a diagram showing the result of simulation of a potentialdistribution when, in a structure in which the peripheral region isprovided with the potential division region, the concentration of theN-type impurity in the peripheral region is held constant, and FIG. 7(b)is a diagram showing the result of simulation of a potentialdistribution in the structure in which, in the structure in which theperipheral region is provided with the potential division region, theconcentration of the N-type impurity in the peripheral region iscontinuously changed;

FIG. 8(a) is a diagram showing the relationship between an excessconcentration in the peripheral region and the breakdown voltage of thesemiconductor device in a structure not provided with a charge balancechange region, and FIG. 8(b) is a diagram showing the relationshipbetween the excess concentration in the peripheral region and thebreakdown voltage of the semiconductor device in the structure providedwith the charge balance change region;

FIG. 9 is a cross-sectional view of a semiconductor device according toa second embodiment of the present disclosure;

FIG. 10(a) is a plan view showing an example of the layout of an SJstructure in a semiconductor device according to a third embodiment ofthe present disclosure, and FIG. 10(b) is a plan view showing anotherexample of the layout of the SJ structure in the semiconductor deviceaccording to the third embodiment;

FIG. 11(a) is a cross-sectional view of a peripheral region in asemiconductor device according to a fourth embodiment of the presentdisclosure, and FIG. 11(b) is a cross-sectional view of the peripheralregion in a semiconductor device not provided with guard rings;

FIG. 12 is a diagram showing the relationship between charges Q trappedbetween an interlayer insulating film and an insulating layer and abreakdown voltage in each of the structures shown in FIG. 11(a) and FIG.11(b);

FIG. 13 is a plan view of a semiconductor device according to a fifthembodiment of the present disclosure;

FIG. 14 is a plan view of a semiconductor device according to a sixthembodiment of the present disclosure;

FIG. 15 is a cross-sectional view of a semiconductor device according toa seventh embodiment of the present disclosure;

FIG. 16 is a plan view of a semiconductor device according to an eighthembodiment of the present disclosure;

FIG. 17(a) is a planar layout diagram of an SJ structure in asemiconductor device according to a ninth embodiment of the presentdisclosure, FIG. 17(b) is a cross-sectional view of the SJ structuretaken along the line XVIIB-XVIIB of FIGS. 17(a), and 17(c) is across-sectional view of the SJ structure taken along the lineXVIIB-XVIIB of FIG. 17(a);

FIG. 18 is a surface layout diagram showing an example of the dimensionsof a P-type column region 5;

FIG. 19(a) is a plan view showing a potential distribution in thesemiconductor device, FIG. 19(b) is a cross-sectional view showing apotential distribution in the semiconductor device, FIG. 19(c) is adiagram showing the distribution of an excess concentration in a crosssection taken along the line XIXC-XIXC of FIG. 19(a), and FIG. 19(d) isa diagram showing the distribution of the excess concentration in across section taken along the line XIXD-XIXD of FIG. 19(b);

FIG. 20 is a view showing the relationship between a charge imbalanceand a breakdown voltage;

FIG. 21 is a planar layout diagram of an SJ structure in a semiconductordevice according to a tenth embodiment of the present disclosure;

FIG. 22(a) is a planar layout diagram of an SJ structure in asemiconductor device according to an eleventh embodiment of the presentdisclosure, FIG. 22(b) is a view showing an impurity concentrationdistribution in an N-type column region in a cross section taken alongthe line XXIIB-XXIIB of FIGS. 22(a), and 22(c) is a diagram showing animpurity concentration distribution in the N-type column region in across section taken along the line XXIIC-XXIIC;

FIG. 23 is a planar layout diagram of an SJ structure in a semiconductordevice according to a twelfth embodiment of the present disclosure;

FIG. 24 is a planar layout diagram of an SJ structure in a semiconductordevice according to a thirteenth embodiment of the present disclosure;

FIG. 25(a) and FIG. 25(b) are plan views each showing a concentrationdistribution in an N-type column region in the vicinity of a cornerportion in an SJ structure according to another embodiment;

FIG. 26(a) and FIG. 26(b) are plan views each showing an excessconcentration distribution in the vicinity of the corner portion in theSJ structure according to the other embodiment; and

FIG. 27 is a view showing the relationship between a charge imbalanceand a breakdown voltage.

EMBODIMENTS FOR CARRYING OUT INVENTION First Embodiment

A semiconductor device according to a first embodiment of the presentdisclosure will be described below with reference to the drawings. Asshown in FIG. 1, the semiconductor device includes a cell region 1 wheresemiconductor elements are formed, and a peripheral region 2. On anouter periphery of the cell region 1 having a quadrilateral shape, theperipheral region 2 is provided so as to surround the cell region 1.

As shown in FIG. 2, in the cell region 1, a large number ofmetal-oxide-film semiconductor field effect transistors (MOSFETs) areformed.

The semiconductor device includes a semiconductor substrate 6 formedwith an SJ structure in which, above an N⁺-type drain layer 3, N-typecolumn regions 4 and P-type column regions 5 are formed as a driftregion and repeatedly arranged in a direction parallel with the planardirection of the drain layer 3.

In addition, above the SJ structure, a P-type layer 7 formed byepitaxial growth is provided. The P-type layer 7 is provided over thecell region 1 and the peripheral region 2. On the other hand, on theside of the drain layer 3 opposite to the SJ structure, a drainelectrode 8 is formed.

In the cell region 1, trench-gate MOSFETs are formed as semiconductorelements 9. Each of the MOSFETs has a typical structure, which will bebriefly described below. A trench 10 is formed to extend through anN⁺-type source region and a P-type channel layer each formed in theP-type layer 7 and reach the N-type column region 4. Over the inner wallsurface of the trench 10, a gate insulating film and a gate layer aresuccessively formed to form a trench-gate structure including the trench10, the gate insulating film, and the gate layer. In the P-type channellayer, a P-type body region is also formed. Note that the structure ofthe MOSFET is illustrative, and another structure may also be used.

The trenches 10 are provided such that the planar directions of planesin which the N-type column regions 4 and the P-type column regions arein contact with each other are parallel with the extending directions inwhich the trenches 10 extend. If it is defined that one of the N-typecolumn regions 4 and the one of the P-type column regions 5 that isadjacent to the N-type column region 4 pair up to form one columnstructure, it follows that the trench gate structure is provided foreach one of the column structures.

In addition, on the gate layer, an interlayer insulating film 11covering the gate layer and provided with contact holes exposing theP-type channel layers is formed. The interlayer insulating film 11 ismade of, for example, local oxidation of silicon (LOCOS). A sourceelectrode 12 is formed so as to cover the interlayer insulating film 11and come in contact with the P-type channel layers via the contactholes.

On the other hand, in the peripheral region 2, the interlayer insulatingfilm 11 is formed on the P-type layer 7. The thickness of the interlayerinsulating film 11 is, for example, 800 nm. On the interlayer insulatingfilm 11, an insulating layer 13 is formed and, on the insulating layer13, a polysilicon layer 14 having a thickness of, for example, 400 nm isformed. The insulating layer 13 is made of, for example, boronphosphorous silicon glass (BPSG). The polysilicon layer 14 is patternedto serve as wiring and, from the cell region 1 side, a gate wire 15 anda field plate 16 are laid out in this order.

The gate wire 15 is electrically connected to the gate layer. On thegate wire 15, a gate electrode 17 is formed. On the field plate 16, arelay electrode 18 electrically connected to the source electrode 12 isformed.

Of the polysilicon layer 14, the portion located outside the field plate16 is formed into a plurality of guard rings 19 which are laid out atequal intervals toward the side opposite to the cell region 1. The guardrings 19 are arranged as, for example, conductive regions in multiplerounds so as to surround the cell region 1. Note that, as the guardrings 19, for example, N-type conductive regions, P-type conductiveregions, metal, or the like may also be used.

Of the polysilicon layer 14, the outermost portion is laid out as anoutermost peripheral ring 20 and, on the outermost peripheral ring 20,an outermost peripheral electrode (EQR) 21 is formed. The outermostperipheral ring 20 is electrically connected to the one of the guardrings 19 that is closest to the outermost peripheral electrode 21.

The outermost peripheral electrode 21 is located closer to the outeredge portion of the semiconductor device, that is, on the outermost edgeportion of the peripheral region 2. The outermost peripheral electrode21 is electrically connected to an N-type epitaxial region locatedaround the drift region via the N⁺-type region 22 provided in the samelayer as the P-type layer 7.

The gate wire 15, the field plate 16, the plurality of guard rings 19,and the outermost peripheral ring 20 are covered with the insulatinglayer 13, and a part of each of the gate wire 15, the field plate 16,and the outermost peripheral ring 20 is exposed from the insulatinglayer 13. The total thickness of the insulating layer 13 is, forexample, 800 nm. The gate electrode 17 and the relay electrode 18 areconnected to the gate wire 15 and the field plate 16 via the openings ofthe insulating layer 13.

The outermost peripheral electrode 21 is provided so as to overlap theSJ structure when viewed from the thickness direction (substrate normaldirection) of the semiconductor substrate 6. As a result, the expansionof a potential distribution in the SJ structure is suppressed by theoutermost peripheral electrode 21.

Of the region of the peripheral region 2 in which the polysilicon layer14 is laid out, the region where the plurality of guard rings 19 arelaid out is used as a potential division region 23. That is, thepotential division region 23 is a region located over the P-type layer 7(on the insulating layer 13 side) to electrically connect the sourceelectrode 12 (relay electrode 18) to the outermost peripheral electrode21 and also divide the voltage between the source electrode 12 (relayelectrode 18) and the outermost peripheral electrode 21 into a pluralityof stages. Note that the length of the peripheral region 2 is, forexample, 250 μm, and the length of the potential division region 23 is,for example, 100 μm.

To divide the voltage into the plurality of stages, the individual guardrings 19 are connected by zener diodes 24 ensuring desired breakdownvoltages. In the present embodiment, the zener diodes 24 are providedsuch that element potentials are distributed in the outer diametricaldirection of the semiconductor device. The breakdown voltage of thezener diode 24 in one stage which connects one of the guard rings 19 tothe guard ring 19 adjacent thereto is, for example, 30 V. Using such azener diode 24, a voltage of, for example, 600 V is divided.

The plurality of guard rings 19 are arranged at equal intervals in thepotential division region 23 from the source electrode 12 (relayelectrode 18) side toward the outermost peripheral electrode 21.Accordingly, the potential division region 23 divides the voltage atequal intervals between the source electrode 12 (relay electrode 18) andthe outermost peripheral electrode 21 into the plurality of stages fromthe source electrode 12 (relay electrode 18) side toward the outermostperipheral electrode 21 side. As a result, it is possible to fixpotentials at equal intervals in the potential division region 23 fromthe source electrode 12 (relay electrode 18) side toward the outermostperipheral electrode 21 side. Thus, a wide margin (charge balancemargin) can be ensured for variations in impurity concentration againstthe deterioration of the breakdown voltages.

Note that the layout in which the guard rings 19 are arranged at equalintervals is illustrative. As long as a potential distribution formed inthe semiconductor substrate 6 in the potential division region 23 can befixed at equal intervals, the guard rings 19 need not be arranged atequal intervals.

As shown in FIG. 3, each of the zener diodes 24 includes N-type regions25 and P-type regions 26 which are alternately arranged along theextending direction of the guard rings 19 between one of the guard rings19 and the other guard ring 19. The N-type regions 25 and the P-typeregions 26 are formed by ion implantation into polysilicon. Since thezener diodes 24 are arranged in series, the potential of the guard ring19 in each stage is divided.

Subsequently, a charge balance in the SJ structure of the semiconductorsubstrate 6 will be described. In the present embodiment, the N-typecolumn regions 4 and the P-type column regions 5, which form the SJstructure, are repeatedly arranged all over the cell region 1 and theperipheral region 2. The depths of the N-type column regions 4 and theP-type column region 5 are, for example, 47 μm and the pitch is 7 μm.

In the cell region 1, the impurity concentration of each of the N-typecolumn regions 4 is the same as the impurity concentration of each ofthe P-type column regions 5. The number of P-carriers is the same as thenumber of N-carriers in the PN-columns. That is, the charge balancecondition is the same in each of the PN-columns. For example, each ofthe impurity concentrations in the N-type column regions 4 and theP-type column regions 5 is 5×10¹⁵ cm⁻³.

On the other hand, the peripheral region 2 is provided with a regionwhere the balance between the respective impurity concentrations in theN-type column regions 4 and the P-type column regions 5 continuouslychanges toward the side opposite to the cell region 1. This region is aregion under the P-type layer 7 (on the drain layer 3 side) and referredto as the charge balance change region 27. Note that the outermostperipheral electrode 21 is located around the charge balance changeregion 27.

Here, in the charge balance change region 27 of the peripheral region 2,the balance between the impurity concentrations continuously changestoward the side opposite to the cell region 1. A description will begiven with reference to FIGS. 4(a) and 4(b). Examples of a planar layoutof the SJ structure located in the peripheral region 2 are shown inFIGS. 4(a) and 4(b). Note that, in FIG. 4, the peripheral region 2 isexpressed as the “N-Rich Region” and the N-type epitaxial region aroundthe drift region is expressed as the “N-Epi region”.

When the direction in which the N-type column regions 4 and the P-typecolumn regions 5 are repeatedly arranged is referred to as a repetitiondirection, in FIG. 4(a), the widths of the P-type column regions 5located in the peripheral region 2 in the repetition direction arereduced at an equal rate to be smaller than the widths of the P-typecolumn regions 5 located in the cell region 1. However, since the widthsof the P-type column region 5 in the peripheral region 2 are constant inthe peripheral region 2, the balance between the impurity concentrationsin the charge balance change region 27 of the peripheral region 2 doesnot change and is constant.

On the other hand, in FIG. 4(b), in the peripheral region 2, the widthsof the P-type column regions 5 in the directions perpendicular to therepetition direction in the planar direction of the drain layer 3continuously decrease toward end portions 5 a of the P-type columnregions 5. That is, the end portions 5 a of the P-type column directions5 taper in the perpendicular directions. In other words, the widths ofthe N-type column regions 4 in the perpendicular directions continuouslyincrease. As a result, in the peripheral region 2, the volume of each ofthe N-type column regions 4 continuously increases with increasingdistance from the cell region 1 so that the balance between the impurityconcentrations shifts toward the N-type in the repetition direction.That is, the N-type predominates and an N-rich state prevails toward theoutermost edge portion of the peripheral region 2. With such a planarlayout of the P-type column regions 5, the balance between the impurityconcentrations in the charge balance change region 27 continuouslychanges.

In the present embodiment, the potential division region 23 is disposedso as to overlap the charge balance change region 27 when viewed fromthe thickness direction of the semiconductor substrate 6.

The present inventors have examined the relationship between the lengthof the potential division region 23 and the breakdown voltage. Theresult thereof is shown in FIG. 5. The “length of the potential divisionregion 23” corresponds to the distance from the end portion of thepotential division region 23 located on the cell region 1 side in theplanar direction of the drain layer 3 to the end portion thereof locatedon the outermost peripheral electrode 21 side.

When FIG. 5 is viewed, the breakdown voltage is stable when the lengthof the potential division region 23 is not less than 50 μm. Here, thelength of 50 μm has a value larger than a depth from the surface of theP-type layer 7 to the drain layer 3.

That is, when the length of the potential division region 23 is short,the breakdown voltage is determined by the peripheral region 2. However,when the length of the potential division region 23 is larger than thedepth from the surface of the P-type layer 7 to the drain layer 3, astable breakdown voltage of not less than 600 V can be obtained, and thebreakdown voltage in the peripheral region 2 can be ensured withcertainty. Accordingly, the length of the potential division region 23described above is larger than the depth from the surface of the P-typelayer 7 to the drain layer 3.

Subsequently, the present inventors have examined the breakdown voltagesof the semiconductor device in the presence/absence of the potentialdivision region 23 in the peripheral region 2 and in thepresence/absence of the charge balance change region 27 in theperipheral region 2. The results thereof are shown in FIG. 6(a) throughFIG. 8(b).

First, FIG. 6(a) and FIG. 6(b) show the result of simulation of apotential distribution in a structure in which the potential divisionregion 23 (guard rings 19 and zener diodes 24) is not provided in theperipheral region 2 and the impurity concentration of each of the N-typecolumn regions 4 is set, for example, 10% higher than the impurityconcentration of each of the P-type column regions 5 in the peripheralregion 2.

FIG. 6(a) shows the result of simulation in a structure in which the SJstructure of the peripheral region 2 has the layout shown in FIG. 4(a).That is, the potential distribution in a structure in which the excessconcentration calculated by excess concentration={(the impurity amountin the N-type column region 4)−(the impurity amount in the P-type columnregion 5)}/(the volume of the column portion) is uniform in theperipheral region 2 is shown. From the result, it can be seen that theequipotential lines are concentrated on the cell region 1 side in theperipheral region 2 and the concentration of an electric field maypossibly occur.

By contrast, FIG. 6(b) shows the result of simulation in a structure inwhich the SJ structure of the peripheral region 2 has the layout shownin FIG. 4(b). That is, FIG. 6(b) shows the result of simulation in thestructure in which the balance between the impurity concentrationscontinuously changes in the charge balance change region 27 of theperipheral region 2. From the result, it can be seen that theequipotential lines change by small degrees from the cell region 1 sideof the peripheral region 2.

The results of simulation of a potential distribution in a structureobtained by providing the guard rings 19 in the structure having apotential distribution as described above are shown in FIG. 7(a) andFIG. 7(b). Since the guard rings 19 are provided, a potential on theguard ring 19 side in the SJ structure is fixed.

FIG. 7(a) shows the result of simulation in a structure obtained byproviding the guard rings 19 in the structure of FIG. 6(a). According tothe result, the equipotential lines in the peripheral region 2 are notsmoothly drawn, and the intervals between the equipotential lines arenon-uniform.

On the other hand, FIG. 7(b) shows the result of simulation in astructure obtained by providing the guard rings 19, which has potentialsfixed at equal intervals, in the structure of FIG. 6(b). According tothe result, the equipotential lines in the SJ structure are smoothlydrawn, and the intervals between the equipotential lines are uniform.

FIG. 8(a) and FIG. 8(b) are diagrams each showing the relationshipbetween the excess concentration in the peripheral region 2 and thebreakdown voltage of the semiconductor device. In each of FIG. 8(a) andFIG. 8(b), the breakdown voltage of a structure not provided with theguard rings 19 is shown by the broken line, and the breakdown voltage ofa structure provided with the guard rings 19 is shown by the solid line.

FIG. 8(a) shows the breakdown voltages in the presence/absence of theguard rings 19 in the structure not provided with the charge balancechange region 27. According to the result, it is understood that adifference is produced in breakdown voltage depending on thepresence/absence of the guard rings 19 irrelevantly to a change in theexcess concentration in the peripheral region 2. This is because, sincea potential distribution in a silicon surface formed by the SJ structurein the peripheral region 2 does not match a surface potentialdistribution defined by the guard rings 19, the potential distributionformed by the SJ structure in the peripheral region 2 is affected. Inthe case of FIG. 8(a), the breakdown voltage has deteriorated in thevicinity of the outermost peripheral ring 20 in the peripheral region 2.

In contrast, FIG. 8(b) shows the breakdown voltages in thepresence/absence of the guard rings 19 in the structure provided withthe charge balance change region 27. According to the result, even whenthe excess concentration in the peripheral region 2 changes, nodifference is produced in breakdown voltage depending on thepresence/absence of the guard rings 19. By matching the potentialdistribution in the silicon surface formed by the SJ structure of theperipheral region 2 and the surface potential distribution defined bythe guard rings 19, it is possible to ensure a wide margin (chargebalance margin) for variations in impurity concentration against thedeterioration of the breakdown voltage. In the present embodiment, byproviding the structure in which the balance between the impurityconcentrations in the peripheral region 2 continuously changes and alsoarranging the guard rings 19 at equal intervals as described above, thesurface potential distributions in the SJ structure in the peripheralregions 2 are equal intervals.

Next, a method of manufacturing the semiconductor device including thecharge balance change region 27 in the semiconductor substrate 6 andincluding the potential division region 23 on the interlayer insulatingfilm 11 will be described. First, the semiconductor substrate 6including the SJ structure is prepared. Here, in the preparedsemiconductor substrate 6, the SJ structure corresponding to theperipheral region 2 has the planar layout of FIG. 4(b) to cause thebalance between the impurity concentrations in the charge balance changeregion 27 in the peripheral region 2 continuously change.

Then, the semiconductor elements in the cell region 1 are formed by atypical semiconductor process. Additionally, in the semiconductorsubstrate 6, the P-type layer 7 is formed on the outer periphery of thecell region 1, and the interlayer insulating film 11 is formed above theP-type layer 7.

Thereafter, above the interlayer insulating film 11, the insulatinglayer 13 and the polysilicon layer 14 are formed, and the polysiliconlayer 14 is laid out into the gate wire 15, the field plate 16, theplurality of guard rings 19, and the outermost peripheral ring 20. Thepolysilicon layer 14 is also left so as to provide coupling between theindividual guard rings 19. Here, the individual guard rings 19 are laidout such that the plurality of guard rings 19 located in the potentialdivision region 23 are located above the charge balance change region27.

Then, ion implantation is performed into the polysilicon layer 14located between the individual guard rings 19 to alternately form theN-type regions 25 and the P-type regions 26 along the extendingdirection of the guard rings 19. Subsequently, the insulating layer 13is further formed so as to cover each of the guard rings 19, the N-typeregions 25, and the P-type regions 26 and parts of the insulating layer13 are opened. The source electrode 12, the gate electrode 17, the relayelectrode 18, and the outermost peripheral electrode 21 aresimultaneously formed all over the cell region 1 and the peripheralregion 2. Thus, the semiconductor device shown in FIG. 1 through FIG. 3is completed.

As described heretofore, the present embodiment is characterized in thatthe peripheral region 2 is provided with the charge balance changeregion 27 where the balance between the impurity concentrationscontinuously changes, and the potential division region 23 which dividesthe voltage between the source electrode 12 and the drain electrode 18into a plurality of parts is provided above the charge balance changeregion 27.

Since the potential division region 23 is located above the chargebalance change region 27 where the impurity concentrations continuouslychange, it is possible to achieve a shielding effect against theinfluence of charges trapped between the interlayer insulating film 11and the insulating layer 13 in the peripheral region 2 and consequentlyprevent fluctuations in breakdown voltage. Therefore, it is possible toensure the breakdown voltage without causing concentration of anelectric field on the peripheral region 2.

Note that the N-type column regions 4 are an example offirst-conductivity-type column regions and the P-type column regions 5are an example of second-conductivity-type column regions. Also, thesource electrode 12 is an example of an element electrode.

Second Embodiment

A semiconductor device according to a second embodiment of the presentdisclosure will be described with reference to FIG. 9. In FIG. 9, thewires between the electrodes and the zener diodes 24 are omitted.

As shown in FIG. 9, in the present embodiment, the individual guardrings 19 extending in directions perpendicular to the direction in whichthe N-type column regions 4 and the P-type column regions 5 arerepeatedly provided in the planar direction of the drain layer 3 overlapthe respective P-type column region 5 when viewed from the thicknessdirection of the semiconductor substrate 6. Thus, the end portions ofthe guard rings 19 may also be located above the P-type column regions5.

Third Embodiment

A semiconductor device according to a third embodiment of the presentdisclosure will be described with reference to FIG. 10(a) and FIG.10(b). As shown in FIG. 10(a) and FIG. 10(b), in the peripheral region2, the N-type column regions 4 and the P-type column regions 5, whichform the SJ structure, are laid out in a ring shape (multi-round frameshape) surrounding the cell region 1. Toward the side opposite to thecell region 1, the N-type column regions 4 and the P-type column regions5 are repeatedly arranged.

Here, in FIG. 10(a), in the repetition direction in which the N-typecolumn regions 4 and the P-type column regions 5 are repeatedlyarranged, the respective widths of the N-type column regions 4 and theP-type column regions 5 are constant and the N-type column regions 4 arearranged at equal intervals. In the placement, there is no change in thebalance between the impurity concentrations in the charge balance changeregion 27 of the peripheral region 2.

On the other hand, in FIG. 10(b), the widths of the N-type columnregions 4 in the charge balance change region 27 increase withincreasing distance from the cell region 1. In other words, withincreasing distance from the cell region 1, the intervals of the P-typecolumn regions 5 increase. As a result, carriers increase in the N-typecolumn regions 4 so that the charge balance change region 27 is in anN-rich state. In this manner, it is possible to continuously change thebalance between the impurity concentrations in the charge balance changeregion 27.

Fourth Embodiment

A semiconductor device according to a fourth embodiment of the presentdisclosure will be described. In each of the embodiments describedabove, the individual guard rings 19 are connected to each other withthe zener diodes 24 which are the potential division elements. However,in the present embodiment, the individual guard rings 19 are connectedwith resistors.

FIG. 11(a) is a cross-sectional view in the peripheral region 2 of thesemiconductor device according to the present embodiment. As shown inthe drawing, in the present embodiment, the gate electrode 17 and thedrain electrode 8 are subjected to potential division using thepotential division region 23. As potential division elements, resistors28 are used. The resistance value of each of the resistors 28 is, forexample, 1×10¹⁰Ω.

The present inventors have examined the breakdown voltages in thepresence/absence of the potential division region 23 in the structure ofthe peripheral region 2 shown in FIG. 11(a). The result thereof is shownin FIG. 12. FIG. 12 shows the relationship between charges Q trappedbetween the interlayer insulating film 11 and the insulating layer 13and the breakdown voltage. As shown in FIG. 12, in the structure notprovided with the potential division region 23 shown in FIG. 11(b), thebreakdown voltage unstably changes in response to the presence of thecharges Q. It has been found that, on the other hand, in a structureprovided with the potential division region 23 as shown in FIG. 11(a), aconstant breakdown voltage can be obtained without depending on thepresence of the charges Q.

Note that, also in the structure using the zener diodes 24 as thepotential division elements, the same effect as obtained in FIG. 12 hasbeen obtained.

Thus, as the potential division elements, the resistors 28 may also beused. By reducing the impurity concentrations when the zener diodes 24shown in the first embodiment are formed, the N-type regions 25 and theP-type impurity regions 26 which form the zener diodes 24 can be used asthe resistors 28.

Since the voltage between the gate electrode 17 and the drain electrode8 is divided, the relay electrode 18 for connecting the guard rings 19to the source electrode 12 is no longer needed. Accordingly, thesemiconductor device can be downsized.

Note that the gate electrode 17 is an example of the element electrode.

Fifth Embodiment

A semiconductor device according to a fifth embodiment of the presentdisclosure will be described with reference to FIG. 13. As shown in FIG.13, in the present embodiment, the one guard ring 19 is disposed in aspiral shape. Accordingly, potentials of the respective stages can bedivided using the resistive component of the guard ring 19.

Sixth Embodiment

A semiconductor device according to a sixth embodiment of the presentdisclosure will be described with reference to FIG. 14.

As shown in FIG. 14, in the present embodiment, a layout has a patternin which the P-type column regions 5 are scattered in a dotted-shape inthe N-type column region 4. That is, the N-type column region 4 and theP-type column region 5 are alternately and repeatedly arranged in aradial direction from the center of the cell region 1. The ratio of theP-type column regions 5 formed in the peripheral region 2 is set lowerthan the ratio of the P-type column regions 5 formed in the cell region1 and is reduced toward the outer peripheral direction of the cellregion 1.

Even when the P-type column regions 5 are formed in the dotted-shape inthe N-type column region 4, the charge balance change region 27 can beconfigured and the same effect as obtained in the first embodiment canbe obtained.

Seventh Embodiment

A semiconductor device according to a seventh embodiment of the presentdisclosure will be described with reference to FIG. 15.

As shown in FIG. 15, it is also possible to form the N-type columnregions 4 and the P-type column regions 5 up to the front surface of thesemiconductor substrate 6 and form the P-type layer 7 not by epitaxialgrowth, but by ion implantation.

When the P-type layer 7 is formed by ion implantation, the N-type columnregions 4 are formed up to the front surface of the semiconductorsubstrate 6. Therefore, it is possible to achieve electrical connectionbetween the N-type epitaxial region around the drift region and theoutermost peripheral electrode 21 without forming the N⁺-type region 22(see FIG. 2) shown in the first embodiment.

Eighth Embodiment

A semiconductor device according to an eighth embodiment of the presentdisclosure will be described with reference to FIG. 16.

As shown in FIG. 16, in the semiconductor device of the presentembodiment, in the column repetition direction, the pitch between theindividual columns is held constant with distance from the cell region 1toward the outer peripheral direction without being changed, while thewidths of the P-type column regions 5 are reduced with distance from thecell region 1 toward the outer peripheral direction. Also, in adirection perpendicular to the repetition direction, the end portions 5a of the P-type column regions 5 are tapered, and the taper angles ofthe tapered portions are reduced with decrease in the widths of theP-type column regions 5, that is, toward the outer peripheral directionof the cell region 1 in the repetition direction.

Since the taper angles of the end portions 5 a are reduced with decreasein the widths of the P-type column regions 5, it is possible to restrictan electric field from being concentrated on corner portions when thewhole SJ structure is assumed to have a quadrilateral shape (hereinafterreferred to simply as the corner portions of the SJ structure).

Also, by gradually decreasing the widths of the P-type column regions 5,it is possible to continuously change the balance between the impurityconcentrations in the N-type column regions 4 and the P-type columnregions 5 with distance from the cell region 1 toward the outerperipheral direction.

Even when the widths of the P-type column regions 5 are changed in thecolumn repetition direction, the N-type impurity concentration can becontinuously changed to be larger than the P-type impurity concentrationwith distance from the cell region 1 toward the outer peripheraldirection, while the peripheral region 2 is provided as an N-rich regionwhere N-type carriers are dominant. As a result, the same effect asobtained in the first embodiment can be obtained.

Ninth Embodiment

A semiconductor device according to a ninth embodiment of the presentdisclosure will be described with reference to FIG. 17(a) and FIG.17(b).

As shown in FIG. 17(a), in the present embodiment, a lateral directionover a paper sheet with FIG. 17(a) is assumed to be a longitudinaldirection (hereinafter referred to as a column longitudinal direction),and the N-type column regions 4 and the P-type column regions 5, whichform the SJ structure, are repeatedly and alternately arranged all overthe cell region 1 and the peripheral region 2 in a directionperpendicular to the column longitudinal direction (hereinafter thedirection perpendicular to the column longitudinal direction is referredto as a column repetition direction).

In the cell region 1, the ratio between the charge amount in the P-typecolumn regions 5 and the charge amount in the N-type column regions 4 isset to 1:1. The depths (column depths) of the N-type column regions 4and the P-type column regions 5 are set to, for example, 45 μm, and acolumn pitch as a repetition unit of the PN columns is set to 6.0 μm.

Also, as shown in FIG. 17(c), the boundary surface between the N-typecolumn region 4 and the P-type column region 5 is formed as a taperedsurface which is inclined in the depth direction to show a tapered shapewhich is narrowed with depth of the P-type column region 5. The angle(hereinafter referred to as a first taper angle) between a boundaryline, which is included in the boundary surface formed as the taperedsurface and passes through a cut surface along the column repetitiondirection, and the column repetition direction is set to, for example,89.6°.

The impurity concentrations in the N-type column regions 4 and theP-type column regions 5 are equalized to equalize the P-type chargeamount and the N-type charge amount in the adjacent PN columns as awhole and provide the same charge balance condition in the PN columns.For example, the impurity concentration in each of the N-type columnregions 4 and the P-type column regions 5 is set to 8.0×10¹⁵ cm⁻³.

Note that, since the boundary surface between the N-type column region 4and the P-type column region 5 is formed as the tapered surface, acharge balance change structure in which the N-type charge amount in theN-type column regions 4 gradually increases to be larger than the P-typecharge amount in the P-type column regions 5 in the depth direction isprovided. However, the P-type charge amount and the N-type charge amountare equalized in the N-type column regions 4 and the P-type columnregions 5 throughout the entire depths thereof. As a result, in the cellregion 1, a charge balance change structure in which the same chargebalance condition is provided in the PN columns as a whole and theN-type charge amount gradually increases to be larger than the P-typecharge amount in the depth direction is provided.

On the other hand, the peripheral region 2 is provided with a regionwhere the balance between the charge amounts in the N-type columnregions 4 and the P-type column regions 5 continuously changes withdistance from the cell region 1 toward the outer peripheral direction.The region is provided under the P-type layer 7 (on the drain layer 3side) to serve as the charge balance change region 27 where the chargebalance is changed. Note that the outermost peripheral electrode 21 islocated around the charge balance change region 27.

In the charge balance change region 27, in the column longitudinaldirection and the column repetition direction, the balance between thecharge amounts in the N-type column regions 4 and the P-type columnregions 5 is continuously changed with distance from the cell region 1toward the outer peripheral direction using different structures.Specifically, the ratio of the volume of the N-type column region 4 tothe volume of the P-type column region 5 is increased to provide theperipheral region 2 as the N-rich region where the N-type charge amountis dominant, while the N-type charge amount is continuously changed tobe larger than the P-type charge amount with distance from the cellregion 1 toward the outer peripheral direction.

In the column longitudinal direction, as shown in FIG. 17(a), theboundary line between the N-type column region 4 and the P-type columnregion 5 in a substrate horizontal plane is inclined with respect to thecolumn repetition direction to show a tapered shape in which the widthsof the P-type column regions 5 gradually decreases. The angle(hereinafter referred to as a second taper angle) formed between theboundary line and the column repetition direction is set to, forexample, 89.8°. The second taper angle is set larger than the firsttaper angle (the second taper angle>the first taper angle). By settingthe second taper angle larger than the first taper angle, the intervalsbetween the equipotential lines are larger in the peripheral region 2than in the cell region 1 to reduce the concentration of an electricfield. Accordingly, the breakdown voltage can be higher in theperipheral region 2 than in the cell region 1.

As shown in FIG. 18, in the P-type column region 5, a portion located inthe cell region 1 and having a constant width has a dimension of 6000 μmin the column longitudinal direction and a dimension of 3.3 μm in thecolumn repetition direction and a portion having a gradually reducedwidth has a dimension of 100 μm in the column longitudinal direction anda dimension of 2.6 μm in the column repetition direction. Thus, in thecolumn longitudinal direction, by changing the width of the P-typecolumn region 5, the balance between the charge amounts in the N-typecolumn regions 4 and the P-type column regions 5 is continuously changedwith distance from the cell region 1 toward the outer peripheraldirection.

Note that the depths of the P-type column regions 5 may be set equal inthe cell region 1 and the peripheral region 2. However, as shown in FIG.17(b), in the present embodiment, the depths are gradually smaller withdistance from the cell region 1 toward the outer periphery. Since theP-type column regions 5 are configured by forming trenches in the N-typecolumn region 4 and then embedding P-type layers therein, reductions inthe widths of the P-type column regions 5 cause a micro-loading effectso that the depths are shallower with reductions in the widths.

In the column repetition direction, the dimensions of the P-type columnregions 5 are prevented from changing from those in the cell region 1,while the column pitch thereof is increased to be larger than the columnpitch in the cell region 1 with distance from the cell region 1 towardthe outer peripheral direction. By gradually increasing the columnpitch, the balance between the charge amounts in the N-type columnregions 4 and the P-type column regions 5 is continuously changed withdistance from the cell region 1 toward the outer peripheral direction.

In the present embodiment, the potential division region 23 is disposedso as to overlap the charge balance change region 27 in the thicknessdirection of the semiconductor substrate 6.

In a semiconductor device having such a configuration, a potentialdistribution and the distribution of the excess concentration (theexcess concentration=(the P-type charge amount−the N-type chargeamount)/the column pitch) are as shown in FIG. 19(a) through FIG. 19(d).Since the charge balance change region 27 is provided, as shown in FIG.19(c) and FIG. 19(d), the excess concentration in each of the XIXC-XIXCcross section and the XIXD-XIXD cross section in FIG. 19(a) and FIG.19(b) decreases with distance from the cell region 1 toward the outerperipheral direction and decreases with the depth in the depthdirection. Consequently, as shown in FIG. 19(a) and FIG. 19(b), theintervals between the equipotential lines shown by the broken lines inthe drawings are larger in the peripheral region 2 than in the cellregion 1 to reduce the concentration of the electric field. Accordingly,it is possible to set the breakdown voltage higher in the peripheralregion 2 than in the cell region 1.

As a result, as can be seen from the diagram of the relationship betweenthe charge imbalance and the breakdown voltage shown in FIG. 20, thebreakdown voltage is not lower even on the outer peripheral side of theperipheral region 2 than in the cell region 1, and the peripheral region2 does not reduce a charge balance margin in the cell region 1.Therefore, it is possible to provide a semiconductor device in which theperipheral region 2 is restricted from reducing the charge balancemargin in the cell region 1 and a breakdown voltage yield can beimproved.

In the front end portion of the P-type column region 5, in an idealequipotential distribution, the equipotential lines terminate one afteranother on the front surface side, as shown in FIG. 17(b). In contrast,in the present embodiment, the depths of the P-type column regions 5 aregradually shallower with the distance from the cell region 1 toward theouter periphery to allow the shapes of the P-type column regions 5 to becloser to the shape of the ideal equipotential distribution. Therefore,it is possible to further reduce the concentration of the electric fieldand further improve the breakdown voltage.

Tenth Embodiment

A semiconductor device according to a tenth embodiment of the presentdisclosure will be described with reference to FIG. 21. The presentembodiment is obtained by modifying a manner of changing the chargebalance in the column repetition direction with respect to the ninthembodiment and is otherwise the same as the ninth embodiment. Thus, adescription will be given only of a portion different from that in theninth embodiment.

As shown in FIG. 21, in the semiconductor device of the presentembodiment, in the column repetition direction, the column pitch is heldconstant without being changed with distance from the cell region 1toward the outer peripheral direction, while the widths of the P-typecolumn regions 5 are reduced with distance from the cell region 1 towardthe outer peripheral direction. By gradually reducing the widths of theP-type column regions 5, the balance between the charge amounts in theN-type column regions 4 and the P-type column regions 5 is continuouslychanged with distance from the cell region 1 toward the outer peripheraldirection.

Even when the widths of the P-type column regions 5 are changed in thecolumn repetition direction, it is possible to provide the peripheralregion 2 as the N-rich region where the N-type charge amount is dominantand also continuously change the N-type charge amount such that theN-type charge amount is larger than the P-type charge amount withdistance from the cell region 1 toward the outer peripheral direction.Therefore, the same effect as obtained in the ninth embodiment can beobtained.

Eleventh Embodiment

A semiconductor device according to an eleventh embodiment of thepresent disclosure with reference to FIG. 22(a) through FIG. 22(c). Thepresent embodiment is obtained by modifying the SJ structure in theninth embodiment and is otherwise the same as the ninth embodiment.Thus, a description will be given only of a portion different from thatin the ninth embodiment.

As shown in FIG. 22(a), in the present embodiment, the lateral directionover a paper sheet with FIG. 22(a) is assumed to be the columnlongitudinal direction, and the widths of the P-type column regions 5are held constant from the cell region 1 to the peripheral region 2 inthe column longitudinal direction. However, in the peripheral region 2,the impurity concentration in the N-type column regions 4 is changed inthe column longitudinal direction and the column repetition directionsuch that the charge amount in the N-type column regions 4 increaseswith distance from the cell region 1 toward the outer peripheraldirection.

Even when the impurity concentration in the N-type column regions 4 areincreased with distance from the cell region 1 toward the outerperipheral direction, it is possible to provide the peripheral region 2as the N-rich region where the N-type charge amount is dominant and alsocontinuously change the N-type charge amount such that the N-type chargeamount is larger than the P-type charge amount with distance from thecell region 1 toward the outer peripheral direction. Therefore, the sameeffect as obtained in the ninth embodiment can be obtained.

Twelfth Embodiment

A semiconductor device according to a twelfth embodiment of the presentdisclosure will be described with reference to FIG. 23. The presentembodiment is obtained by modifying the SJ structure in the peripheralregion 2 in the ninth embodiment and is otherwise the same as the ninthembodiment. Accordingly, a description will be given only of a portiondifferent from that in the ninth embodiment.

As shown in FIG. 23, in the present embodiment, the cell region 1 isprovided with a SJ structure in which the lateral direction over a papersheet with FIG. 23 is assumed to be the column longitudinal direction, adirection perpendicular to the column longitudinal direction is assumedto be the column repetition direction, and the N-type column regions 4and the P-type column regions 5 are repeatedly arranged. On the otherhand, in the peripheral region 2, the P-type column regions 5 areprovided in a multi-round frame shape so as to surround the periphery ofthe cell region 1. In the case of the present embodiment, because thecell region 1 has a quadrilateral shape, the P-type column regions 5 inthe peripheral region 2 also have quadrilateral frame shapes and haverounded corner portions so as to allow a reduction in the concentrationof an electric field in the corner portions.

In such a structure, the intervals between the P-type column regions 5arranged in the multi-round frame shape are increased toward the outerperipheral direction of the cell region 1. Thus, the charge amount inthe N-type column regions 4 is increased with distance from the cellregion 1 toward the outer peripheral direction.

Even when the intervals between the P-type column regions 5 arranged inthe multi-round frame shape are increased toward the outer peripheraldirection of the cell region 1, it is possible to provide the peripheralregion 2 as the N-rich region where the N-type charge amount is dominantand also continuously change the N-type charge amount such that theN-type charge amount is larger than the P-type charge amount withdistance from the cell region 1 toward the outer peripheral direction.Therefore, the same effect as obtained in the ninth embodiment can beobtained.

Thirteenth Embodiment

A semiconductor device according to a thirteenth embodiment of thepresent disclosure will be described with reference to FIG. 24. Thepresent embodiment is obtained by modifying the SJ structure in theninth embodiment and is otherwise the same as the ninth embodiment.Accordingly, a description will be given only of a portion differentfrom that in the ninth embodiment.

As shown in FIG. 24, in the present embodiment, in both of the cellregion 1 and the peripheral region 2, the P-type column regions 5 arescattered in a dotted shape. In the cell region 1, the column ratiobetween the N-type column regions 4 and the P-type column regions 5 isset to 1:1. On the other hand, in the peripheral region 2, the ratio ofthe P-type column regions 5 formed therein is set lower than the ratioof the P-type column regions 5 formed in the cell region 1 and isgradually reduced with distance from the cell region 1 toward the outerperipheral direction. Thus, the charge amount in the N-type columnregions 4 is increased with distance from the cell region 1 toward theouter peripheral direction.

By providing such a configuration, even when an SJ structure does notinclude striped PN columns, but a structure in which the P-type columnregions 5 are arranged in the dotted shape is provided, it is possibleto provide the peripheral region 2 as the N-rich region where the N-typecharge amount is dominant and also continuously change the N-type chargeamount such that the N-type charge amount is larger than the P-typecharge amount with distance from the cell region 1 toward the outerperipheral direction. Therefore, the same effect as obtained in theninth embodiment can be obtained.

Other Embodiments

The configuration of the semiconductor device shown in each of theforegoing embodiments is illustrative. The semiconductor device is notlimited to the configurations described above and may also have anotherconfiguration capable of implementing the present disclosure. Forexample, the semiconductor elements are not limited to the MOSFETs andmay also be diodes or the like. The MOSFETs may also be of planar types,not the trench-gate types.

Also in a structure in which the resistors 28 are used as the potentialdivision elements, the N-type column regions 4 in the charge balancechange region 27 are not limited to the layout shown in FIG. 4(b) andmay also have the layout shown in FIG. 10(b).

In each of the foregoing embodiments, the entire potential divisionregion 23 overlaps the charge balance change region 27 when viewed fromthe thickness direction of the semiconductor substrate 6. However, thisis an example of the placement, and at least a part of the potentialdivision region 23 may appropriately overlap the peripheral region 2,preferably the charge balance change region 27 when viewed from thethickness direction of the semiconductor substrate 6. That is, when thepotential division region 23 is disposed at least over the peripheralregion 2, it is possible to achieve a shielding effect against theinfluence of the charges trapped in the peripheral region 2 andconsequently prevent variations in breakdown voltage. Accordingly, it ispossible to ensure the breakdown voltage without allowing an electricfield to be concentrated on the peripheral region 2. When the potentialdivision region 23 is provided so as to overlap the charge balancechange region 27, it is possible to match the potential distribution inthe silicon surface and the surface potential distribution defined bythe guard rings 19 so that no difference is produced in breakdownvoltage depending on the presence/absence of the guard rings. As aresult, the effect of being able to ensure a wider charge balance marginagainst the deterioration of the breakdown voltage can be obtained.

In the first embodiment, the structure in which the voltage between theoutermost peripheral electrode 21 (drain electrode 8) and the sourceelectrode 12 is divided in the potential division region 23 is provided.However, the structure may also be such that the voltage between theoutermost peripheral electrode 21 (drain electrode 8) and the gateelectrode 17 is divided in the same manner as in the fourth embodiment.Accordingly, a lead-out electrode from the gate can be used, a regionfor the relay electrode 18 which leads out an electrode from the sourceis unnecessary, and an area of the semiconductor device can be reducedby the region.

Also, in the first embodiment, the potential division is performed usingthe zener diodes 24 as the potential division elements. However, in thesame manner as in the fourth embodiment, the resistors 28 may also beused.

In each of the foregoing embodiments, the balance between the impurityconcentrations continuously changes in the charge balance change region27. However, the continuous changing of the balance between the impurityconcentrations may also be started from a region of the peripheralregion 2 located closer to the cell region 1 than the charge balancechange region 27. That is, the charge balance change region 27 of theperipheral region 2 may also be adjacent to the cell region 1. As aresult, the equipotential lines start to be curved on the cell region 1side to restrict a difference between the amount of carriers supplied tothe cell region 1 and the amount of carriers supplied to the peripheralregion 2 when a high carrier-injected state has occurred. Depending onthe structure of the charge balance change region 27, it may also bepossible to change the N-type impurity concentration in the N-typeepitaxial region located around the drift region.

For example, in the structure shown in FIG. 4(b), the widths of theP-type column regions 5 arranged in the repetition direction are heldconstant and the taper angles of the end portions 5 a each having atapered shape are also held constant. In addition, the pitch between theP-type column regions 5 is increased toward the outer peripheraldirection of the cell region 1 in the repetition direction. In the caseof providing such a structure, in both of the repetition direction andthe direction perpendicular to the repetition direction, the ratio ofthe N-type impurity concentration to the P-type impurity concentrationincreases toward the outer peripheral direction of the cell region 1.

Accordingly, when the ratio of the N-type impurity concentration isincreased in the corner portions of the SJ structure using the same rateas used to increase the ratio of the N-type impurity concentration inthe repetition direction and the direction perpendicular to therepetition direction, the ratio of the N-type impurity concentration ishigher than in the other portion of the charge balance change region 27.That is, the corner portions have the ratio obtained by multiplying theratio of the N-type impurity concentration in the repetition directionby the ratio of the N-type impurity concentration in the directionperpendicular to the repetition direction so that the ratio of theN-type impurity concentration undesirably becomes higher.

Accordingly, in the case of the structure shown in FIG. 4(b), the ratioof the N-type impurity concentration may be set appropriately for thecorner portions by connecting the portions having the same ratios of theN-type impurity concentration in the repetition direction and theportions having the same ratios of the N-type impurity concentrations inthe direction perpendicular to the repetition direction. That is, whenlines showing locations having the same ratios of the N-type impurityconcentrations are defined to be equi-concentration lines, as shown inFIG. 25(a), the equi-concentrations lines may appropriately have taperedshapes in the corner portions. Accordingly, the ratio of the N-typeimpurity concentration can be restricted from becoming higher in thecorner portions than in the other portion of the charge balance changeregion 27.

In the structure shown in FIG. 16, the widths of the P-type columnregions 5 arranged in the repetition direction are gradually reduced,and the taper angles of the end portions 5 a each having a tapered shapeare also gradually reduced. Also, in the repetition direction, the pitchbetween the P-type column regions 5 is held constant. Also in the caseof providing such a structure, the ratio of the N-type impurityconcentration to the P-type impurity concentration increases toward theouter peripheral direction of the cell region 1 in both of therepetition direction and the direction perpendicular to the repetitiondirection. Accordingly, also in this case, the ratio of the N-typeimpurity concentration in the corner portions may be set appropriatelyby connecting the portions having the same ratios of the N-type impurityconcentrations to the P-type impurity concentration in the repetitiondirection and the portions having the same ratios of the N-type impurityconcentrations to the P-type impurity concentration in the directionperpendicular to the repetition direction.

However, compared to the structure of FIG. 4(b), even when the ratio ofthe N-type impurity concentration is increased in the corner portions ofthe SJ structure using the same rate as used to increase the ratio ofthe N-type impurity concentration in the repetition direction and thedirection perpendicular to the repetition direction, the degree of whichthe ratio of the N-type impurity concentration increases is low.Accordingly, as shown in FIG. 25(b), the equi-concentration lines in thecorner portions are provided with shapes each having a curvature whichgradually increases toward the outer peripheral direction of the cellregion 1. Accordingly, the ratio of the N-type impurity concentrationcan be restricted from becoming higher in the corner portions than inthe other portion of the charge balance change region 27.

Note that, in each of the foregoing embodiments, the concentrations ofthe N-type impurity and the P-type impurity forming the N-type columnregions 4 and the P-type column regions 5 are constant and the regions(volumes) in which the N-type column regions 4 and the P-type columnregions 5 are formed are changed toward the outer peripheral directionof the cell region 1 to configure the charge balance change region 27.This is because, when the N-type impurity and the P-type impurityforming the N-type column regions 4 and the P-type column regions 5 haveconstant concentrations, the manufacturing process thereof can be rathersimplified. However, if the manufacturing process of the N-type columnregions 4 and the P-type column regions 5 is performed in a plurality ofseparate steps for the different impurity concentrations, theconcentrations of the N-type impurity and the P-type impurity formingthese can also be changed. Accordingly, it may also be possible tochange the concentrations of the N-type impurity and the P-type impurityforming the N-type column regions 4 and the P-type column regions 5toward the outer peripheral direction of the cell region 1 to configurethe charge balance change region 27.

In short, in the charge balance change region 27, the charge amount maydecrease appropriately toward the outer peripheral direction of the cellregion 1. Accordingly, it may also be possible to, for example, hold theP-type impurity concentration in the P-type column regions 5 constantand also increase the N-type impurity concentration in the N-type columnregions 4 toward the outer peripheral direction of the cell region 1.

Likewise, in the case of a structure in which the P-type column regions5 are scattered in a dotted shape as in the sixth and thirteenthembodiments, it may also be possible to reduce the region (volume) inwhich dots forming the P-type column regions 5 are formed toward theouter peripheral direction of the cell region 1 to configure the chargebalance change region 27.

Also for the SJ structure, it is not limited to the structure describedabove. That is, the structure is appropriate as long as, in the cellregion 1, the P-type charge amount and the N-type charge amount in theadjacent PN columns as a whole are equalized, the peripheral region 2 isprovided as the N-rich region where the N-type charge amount isdominant, and the N-type charge amount is continuously changed to belarger than the P-type charge amount with distance from the cell region1 toward the outer peripheral direction.

In each of the foregoing embodiments, the description has been given ofthe case where the first conductivity type is the N-type and the secondconductivity type is the P-type. However, the present disclosure isapplicable even to a semiconductor device in which the firstconductivity type is the P-type and the second conductivity type is theN-type. That is, even to a structure in which the conductivity types ofthe individual members described in each of the foregoing embodimentsare inverted, the present disclosure is applicable.

It is also preferable that, depending on the structure of the chargebalance change region 27, the gradient of the excess concentration inthe corner portions is reduced to be smaller than the gradient of theexcess concentration in the repetition direction and the directionperpendicular to the repetition direction.

For example, in the structure shown in FIG. 17(a), the widths of theP-type column regions 5 arranged in the repetition direction are heldconstant and the taper angle of each of the end portions having thetapered shapes are also held constant. Also, the pitch between theP-type column regions 5 is increased toward the outer peripheraldirection of the cell region 1 in the repetition direction. In the caseof providing such a structure, in both of the repetition direction andthe direction perpendicular to the repetition direction, the excessconcentration decreases toward the outer peripheral direction of thecell region 1.

Accordingly, in the corner portions of the structure shown in FIG.17(a), the gradient of the excess concentration is larger than in thecharge balance change region 27 in the repetition direction and thedirection perpendicular to the repetition direction. That is, in thecorner portions, the excess concentration corresponds to the sum of theexcess concentrations in the repetition direction and in the directionperpendicular thereto so that the gradient of the excess concentrationis larger. When the portions having the same excess concentrations inthe repetition direction and the portions having the same excessconcentrations in the direction perpendicular to the repetitiondirection are connected with lines, the lines showing the locationshaving the same excess concentrations are defined to beequi-excess-concentration lines. In the case of the structure shown inFIG. 17(a), the equi-excess-concentration lines in the corner portionsare as shown in FIG. 27(a). The equi-excess-concentration lines in thecorner portions are denser than in the repetition direction and theperpendicular direction. This indicates that the breakdown voltage inthe corner portions is lower than the breakdown voltages in therepetition direction and the perpendicular direction.

Accordingly, as shown in FIG. 27(b), the column shapes of the P-columnregions 5 and the N-column regions 4 are formed in which the curvaturesgradually increase as the equi-excess-concentration lines in the cornerportions are closer to the outer peripheral direction of the cell region1. As a result, the equi-excess-concentration lines in the cornerportions are sparser than in the repetition direction and theperpendicular direction. This means that the breakdown voltages in thecorner portions are higher than the breakdown voltages in the repetitiondirection and in the perpendicular direction and a more ideal structurecan be provided.

As described above, in each of the foregoing embodiments, theconcentrations of the N-type impurity and the P-type impurity formingthe N-type column regions 4 and the P-type column regions 5 are constantand the regions (volumes) in which the N-type column regions 4 and theP-type column regions 5 are formed are changed toward the outerperipheral direction of the cell region 1 to configure the chargebalance change region 27. Likewise, the regions (volumes) in which theN-type column regions 4 and the P-type column regions 5 are formed arechanged in the depth direction to configure a charge balance changestructure in which the charge balance is changed even in the depthdirection. This is because, when the N-type impurity and the P-typeimpurity forming the N-type column regions 4 and the P-type columnregions 5 have constant concentrations, the manufacturing processthereof can be rather simplified. However, if the manufacturing processof the N-type column regions 4 and the P-type column regions 5 isperformed in a plurality of separate steps for the different impurityconcentrations, the concentrations of the N-type impurity and the P-typeimpurity forming these can also be changed. Accordingly, it may also bepossible to change, as in the eleventh embodiment, the concentrations ofthe N-type impurity and the P-type impurity forming the N-type columnregions 4 and the P-type column regions 5 toward the outer peripheraldirection of the cell region 1 such that the P-type impurityconcentration is lower than the N-type impurity concentration toward theouter peripheral direction to configure the charge balance change region27. Likewise, it may also be possible to change the concentrations ofthe N-type impurity and the P-type impurity forming the N-type columnregions 4 and the P-type column regions 5 in the depth direction suchthat the P-type impurity concentration is lower than the N-type impurityconcentration as the depth increases to change the charge balance.

In short, in the charge balance change region 27, the P-type chargeamount corresponding to the second-conductivity-type charge amount maygradually decrease appropriately toward the outer peripheral directionof the cell region 1 to be smaller than the N-type charge amountcorresponding to the first-conductivity-type charge amount. Also in thedepth direction, the P-type charge amount corresponding to thesecond-conductivity-type charge amount may gradually decreaseappropriately with the increase of the depth to be smaller than theN-type charge amount corresponding to the first-conductivity-type chargeamount. Accordingly, it may also be possible to, for example, hold theP-type impurity concentration in the P-type column regions 5 constantand also increase the N-type impurity concentration in the N-type columnregions 4 toward the outer peripheral direction of the cell region 1.

Note that, in the ninth embodiment, in accordance with the shapes of theN-type column regions 4 and the P-type column regions 5 described in theninth embodiment, the relationship between the N-type charge amount andthe P-type charge amount has been described as the magnituderelationship between the first taper angle and the second taper angle.Specifically, in the ninth embodiment, with regard to the charge balancechange region 27, the second taper angle is set larger than the firsttaper angle to be able to provide the breakdown voltage in theperipheral region 2 which is higher than the breakdown voltage in thecell region 1. However, even when the concentrations of the N-typeimpurity and the P-type impurity forming the structures of the tenth tofourteenth embodiments or the N-type column regions 4 and the P-typecolumn regions 5 are changed toward the outer peripheral direction ofthe cell region 1 or in the depth direction, the same holds true. Thatis, between the first-conductivity-type column regions (the N-typecolumn regions 4) and the second-conductivity-type column regions (theP-type column regions 5), the following relationship may be establishedappropriately.

The repetition unit for the first-conductivity-type column regions(N-type column regions 4) and the second-conductivity-type columnregions (P-type column regions 5) is assumed to be the column pitch.Also, an excess concentration N is assumed to be given by the excessconcentration=(the second-conductivity-type charge amount−thefirst-conductivity-type charge amount)/the column pitch. In this case,the gradient of the excess concentration in the charge balance changeregion 27 in a direction from the cell region 1 toward the outerperipheral direction is assumed to be given by dN/dx=(N1−N2)/x. In thepresent expression, N1 is a concentration obtained by dividing, by thecolumn pitch, the difference between the second-conductivity-type chargeamount (the P-type charge amount in the P-type column regions 5) and thefirst-conductivity-type charge amount (the N-type charge amount in theN-type column regions 4) at a boundary position between the cell region1 and the peripheral region 2, N2 is a concentration obtained bydividing, by the column pitch, the difference between thesecond-conductivity-type charge amount (the P-type charge amount in theP-type column regions 5) and the first-conductivity-type charge amount(the N-type charge amount in the N-type column regions 4) at a front end(outermost peripheral) position in a direction from the cell region 1toward the outer peripheral direction, and x is a distance from anoutermost peripheral position in the second-conductivity-type columnregion in the cell region 1 to the front end position therein in theouter peripheral direction. Also, the gradient of the excessconcentration in the depth direction in the cell region is assumed to begiven by dN/dz=(N3−N4)/z. In the present expression, N3 is aconcentration obtained by dividing, by the column pitch, the differencebetween the second-conductivity-type charge amount (the P-type chargeamount) and the first-conductivity-type charge amount (the N-type chargeamount in the N-type column regions 4) at a surface position in the cellregion 1, N4 is a concentration obtained by dividing, by the columnpitch, the difference between the second-conductivity-type charge amount(the P-type charge amount) and the first-conductivity-type charge amount(the N-type charge amount in the N-type column regions 4) at a deepestposition in the cell region 1, and z is a distance from the surfaceposition to the deepest position in the cell region 1, i.e., the depthof each of the second-conductivity-type column regions.

By satisfying dN/dx≦dN/dz for each of the gradients of the excessconcentrations defined, the intervals between the equipotential linesare wider in the peripheral region 2 than in the cell region 1 and theconcentration of the electric field is reduced. Therefore, it ispossible to provide the breakdown voltage in the peripheral region 2which is higher than the breakdown voltage in the cell region 1.

As for an innermost peripheral position in the charge balance changeregion 27, i.e., a starting point for the change which provides agradient in the changing of the excess concentration, it is not limitedto the boundary position between the cell region 1 and the peripheralregion 2. For example, the starting point for the changing of the excessconcentration may also be located in the peripheral region 2. In theforegoing embodiment, the boundary position between the cell region 1and the peripheral region 2 is assumed to be a position at which thecharge balance region 27 begins and therefore x is defined as thedistance from the boundary position between the cell region 1 and theperipheral region 2 to the outermost periphery of the peripheral region2. However, basically, x is the distance from the innermost peripheralposition in the charge balance change region 27 to the outermostperipheral position therein.

The invention claimed is:
 1. A semiconductor device including a cellregion and a peripheral region surrounding the cell region, thesemiconductor device comprising: a semiconductor substrate including afirst-conductivity-type layer, and first-conductivity-type columnregions and second-conductivity-type column regions formed above thefirst-conductivity-type layer and serving as a drift region, thefirst-conductivity-type column regions and the second-conductivity-typecolumn regions forming a super-junction structure, each of thefirst-conductivity-type column regions having a first-conductivity-typeimpurity concentration per unit volume, each of thesecond-conductivity-type column regions having asecond-conductivity-type impurity concentration per unit volume, a partof the semiconductor substrate being included in the cell region andother part of the semiconductor substrate being included in theperipheral region; a semiconductor element disposed in the cell region;an element electrode of the semiconductor element disposed in the cellregion; an outermost peripheral electrode electrically connected to thesemiconductor substrate in the peripheral region; asecond-conductivity-type layer formed above the super-junction structurein the peripheral region; and a potential division region formed abovethe second-conductivity-type layer to electrically connect the elementelectrode to the outermost peripheral electrode and also divide avoltage between the element electrode and the outermost peripheralelectrode into a plurality of stages, a part of the potential divisionregion overlapping the peripheral region when viewed from a thicknessdirection of the semiconductor substrate, wherein the peripheral regionfurther includes a charge balance change region in which a differencebetween the first-conductivity-type impurity concentration and thesecond-conductivity-type impurity concentration of one section of thecharge balance change region is larger than a difference between thefirst-conductivity-type impurity concentration and thesecond-conductivity-type impurity concentration of another section ofthe charge balance change region, the one section being located fartherfrom the cell region than the another section in the peripheral region.2. The semiconductor device according to claim 1, wherein the potentialdivision region divides the voltage between the element electrode andthe outermost peripheral electrode from the element electrode sidetoward the outermost peripheral electrode side such that a potentialdistribution in the super-junction structure has equal intervals in aradial direction of the cell region on a plane in which thefirst-conductivity-type layer extends.
 3. The semiconductor deviceaccording to claim 1, wherein, in a radial direction of the cell regionon a plane in which the first-conductivity-type layer extends, a lengthof the potential division region from an end portion located on the cellregion side to an end portion located on the outermost peripheralelectrode side is greater than a depth from a surface of thesecond-conductivity-type layer to the first-conductivity-type layer. 4.The semiconductor device according to claim 1, wherein the outermostperipheral electrode overlaps the super-junction structure when viewedfrom the thickness direction of the semiconductor substrate.
 5. Thesemiconductor device according to claim 1, wherein the charge balancechange region is adjacent to the cell region.
 6. The semiconductordevice according to claim 1, wherein the first-conductivity-type columnregions and the second-conductivity-type column regions, which form thesuper-junction structure, are repeatedly arranged in a repetitiondirection in both of the cell region and the peripheral region, andwherein, in the peripheral region, each of the second-conductivity-typecolumn regions has one portion and another portion closer to an endportion of the each of the second-conductivity-type column regions thanthe one portion in a direction perpendicular to the repetition directionin a plane in which the first-conductivity-type layer extends, wherein awidth of the another portion in the direction perpendicular to therepetition direction is smaller than a width of the one portion in thedirection perpendicular to the repetition direction, so that, in thecharge balance change region, the difference between thefirst-conductivity-type impurity concentration and thesecond-conductivity-type impurity concentration of the one section ofthe charge balance change region is larger than the difference betweenthe first-conductivity-type impurity concentration and thesecond-conductivity-type impurity concentration of the another sectionof the charge balance region.
 7. The semiconductor device according toclaim 6, wherein intervals between the first-conductivity-type columnregions and the second-conductivity-type column regions in therepetition direction are same in both of the cell region and theperipheral region, and wherein, in the peripheral region, a width of oneof the second-conductivity-type column regions in the directionperpendicular to the repetition direction is smaller than a width ofanother one of the second-conductivity-type column regions in thedirection perpendicular to the repetition direction, the one of thesecond-conductivity-type regions being located farther from the cellregion than the another one of the second-conductivity-type regions inthe repetition direction, so that, in the charge balance change region,the difference between the first-conductivity-type impurityconcentration and the second-conductivity-type impurity concentration ofthe one section of the charge balance change region is larger than thedifference between the first-conductivity-type impurity concentrationand the second-conductivity-type impurity concentration of the anothersection of the charge balance change region.
 8. The semiconductor deviceaccording to claim 1, wherein, in the peripheral region, thefirst-conductivity-type column regions and the second-conductivity-typecolumn regions, which form the super-junction structure, are laid out ina ring shape surrounding the cell region, while thefirst-conductivity-type column regions and the second-conductivity-typecolumn regions are repeatedly arranged in a repetition direction towarda side opposite to the cell region, and wherein, in the peripheralregion, a width of one of the first-conductivity-type column regions islarger than a width of another one of the first-conductivity-type columnregions, the one of the first-conductivity-type column regions beinglocated farther from the cell region than the another one of thefirst-conductivity-type column regions in the repetition direction. 9.The semiconductor device according to claim 1, wherein thesuper-junction structure is configured such that thesecond-conductivity-type column regions are scattered in a dotted shapein the first-conductivity-type column region, wherein a ratio betweenthe peripheral region and the second-conductivity-type regions formed inthe peripheral region is lower than a ratio between the cell region andthe second-conductivity-type regions formed in the cell region, andwherein a ratio between the peripheral region and thesecond-conductivity-type regions in the one section of the peripheralregion is lower than a ratio between the peripheral region and thesecond-conductivity-type regions in the another section of theperipheral region, the one section being located farther from the cellregion than the another section in the peripheral region in a radialdirection of the cell region.
 10. The semiconductor device according toclaim 1, wherein the super-junction structure is configured such that,in the cell region, the first-conductivity-type column regions and thesecond-conductivity-type column regions are repeatedly and alternatelyformed using a direction parallel with a plane in which thefirst-conductivity-type layer extends as a column longitudinal directionand using a direction perpendicular to the column longitudinal directionas a column repetition direction while, in the peripheral region, thesecond-conductivity-type column regions are formed in a multi-roundframe shape surrounding a periphery of the cell region, and wherein, inthe peripheral region, one interval between the second-conductivity-typecolumn regions configured in the multi round frame shape is larger thananother interval between the second-conductivity-type column regions,the one interval being located farther from the cell region than theanother interval in the peripheral region in a radial direction of thecell region.
 11. A semiconductor device including a cell region in whicha semiconductor element is formed, and a peripheral region surroundingthe cell region, the semiconductor device comprising: a semiconductorsubstrate including a first-conductivity-type layer, andfirst-conductivity-type column regions and second-conductivity-typecolumn regions formed above the first-conductivity-type layer andserving as a drift region, the first-conductivity-type column regionsand the second-conductivity-type column regions forming a super-junctionstructure, each of the first-conductivity-type column regions having afirst-conductivity-type charge, each of the second-conductivity-typecolumn regions having a second-conductivity-type charge, an amount ofthe first-conductivity-type charge per unit volume being defined as afirst-conductivity-type charge amount, an amount of thesecond-conductivity-type charge per unit volume being defined as asecond-conductivity-type charge amount, a part of the semiconductorsubstrate being included in the cell region and other part of thesemiconductor substrate being included in the peripheral region, afirst-conductivity-type charge amount and a second-conductivity-typecharge amount in the super-junction structure being equal in the cellregion, the semiconductor substrate further including a charge balancechange region in the peripheral region, wherein, in the charge balancechange region, the first-conductivity-type charge amount is larger thanthe second-conductivity-type charge amount, and a ratio of thefirst-conductivity-type charge amount to the second-conductivity-typecharge amount in one section of the charge balance change region islarger than a ratio of the first-conductivity-type charge amount to thesecond-conductivity-type charge amount in another section of the chargebalance change region, the one section being located farther from thecell region than the another section in the peripheral region in aradial direction of the cell region.
 12. The semiconductor deviceaccording to claim 11, wherein the super-junction structure isconfigured such that the first-conductivity-type column regions and thesecond-conductivity-type column regions are repeatedly and alternatelyformed using a direction parallel with a plane in which thefirst-conductivity-type layer extends as a column longitudinal directionand using a direction perpendicular to the column longitudinal directionas a column repetition direction, and wherein each of thesecond-conductivity-type column regions has a front end portion in thecolumn longitudinal direction, and the front end portion is formed in ataper shape having a tapering width such that a boundary surface withthe first-conductivity-type column region becomes a taper shape inclinedwith respect to the column repetition direction.
 13. The semiconductordevice according to claim 12, wherein, in the super-junction structure,widths of the second-conductivity-type column regions in the columnrepetition direction are equal in the cell region and the peripheralregion, wherein column pitches, which are repetition units of thefirst-conductivity-type column regions and the second-conductivity-typecolumn regions, are equal in the cell region, wherein the column pitchesin the peripheral region are larger than the column pitches in the cellregion, and wherein, in the peripheral region, one of the column pitchesis larger than another one of the column pitches, the one of the columnpitches being located farther from the cell region than the another oneof the column pitches in the peripheral region in the column repetitiondirection.
 14. The semiconductor device according to claim 12, wherein awidth of one of the second-conductivity-type column regions is smallerthan a width of another one of the second-conductivity-type columnregions, the one of the second-conductivity-type column regions beinglocated farther from the cell region than the another one of thesecond-conductivity-type column regions in the column repetitiondirection, and wherein column pitches, which are repetition units of thefirst-conductivity-type column regions and the second-conductivity-typecolumn regions, are equal in the cell region and the peripheral region.15. The semiconductor device according to claim 12, wherein a depth ofone portion in each of the second-conductivity-type column regions issmaller than a depth of another portion in each of thesecond-conductivity-type column regions, the one portion being locatedfarther from the cell region than the another portion in each of thesecond-conductivity-type column regions in the column longitudinaldirection.
 16. The semiconductor device according to claim 11, wherein,in the peripheral region, a first-conductivity-type impurityconcentration per unit volume of one portion in each of thefirst-conductivity-type column regions is larger than afirst-conductivity-type impurity concentration per unit volume ofanother portion in each of the first-conductivity-type column regions,the one portion being farther from the cell region than the anotherportion in each of the first-conductivity-type column regions.
 17. Thesemiconductor device according to claim 11, wherein the super-junctionstructure is configured such that, in the cell region, thefirst-conductivity-type column regions and the second-conductivity-typecolumn regions are repeatedly and alternately formed using a directionparallel with a plane in which the first-conductivity-type layer extendsas a column longitudinal direction and using a direction perpendicularto the column longitudinal direction as a column repetition directionwhile, in the peripheral region, the second-conductivity-type columnregions are configured in a multi-round frame shape surrounding aperiphery of the cell region, and wherein, in the peripheral region, oneinterval between the second-conductivity-type column regions configuredin the multi round frame shape is larger than another interval betweenthe second-conductivity-type column regions, the one interval beinglocated farther from the cell region than the another interval in theperipheral region in a radial direction of the cell region.
 18. Thesemiconductor device according to claim 11, wherein the super-junctionstructure is configured such that the second-conductivity-type columnregions are scattered in a dotted shape in the first-conductivity-typecolumn region, and wherein a ratio between the peripheral region and thefirst-conductivity-type regions formed in the peripheral region is lowerthan a ratio between the cell region and the first-conductivity-typeregions formed in the cell region, and wherein a ratio between theperipheral region and the first-conductivity-type regions in the onesection of the peripheral region is lower than a ratio between theperipheral region and the first-conductivity-type regions in the anothersection of the peripheral region, the one section being located fartherfrom the cell region than the another section in the peripheral regionin a radial direction of the cell region.
 19. The semiconductor deviceaccording to claim 11, wherein the super-junction structure includes acharge balance change structure in which a ratio of thefirst-conductivity-type charge amount to the second-conductivity-typeamount of one section of the charge balance change structure is largerthan a ratio of the first-conductivity-type charge amount to thesecond-conductivity type charge amount of another section of the chargebalance change structure, the one section being located deeper than theanother section, and wherein when a repetition unit of thefirst-conductivity-type column regions and the second-conductivity-typecolumn regions is defined as a column pitch and an excess concentrationN is given by the excess concentration N=(the second-conductivity-typecharge amount−the first-conductivity-type charge amount)/the columnpitch), a concentration change gradient dN/dx=(N1−N2)/x of the excessconcentration in the charge balance change region toward the outerperipheral direction when N1 is the excess concentration at an innermostperipheral position in the charge balance change region, N2 is theexcess concentration at an outermost peripheral position in the chargebalance change region extending from the cell region toward the outerperipheral direction, and x is a distance from the innermost peripheralposition to the outermost peripheral position in the charge balancechange region and a concentration change gradient dN/dz=(N3−N4)/z of theexcess concentration in the depth direction in the charge balance changestructure when N3 is the excess concentration at a surface position inthe cell region, N4 is the excess concentration at a deepest position inthe cell region, and z is a distance from the surface position to thedeepest position in the cell region to satisfy a relationship ofdN/dx≦dN/dz.
 20. The semiconductor device according to claim 19, whereinthe excess concentration N2 at the outer periphery of the peripheralregion and the excess concentration N4 at the deepest position in thecell region satisfy a relationship of N2>N4.